Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations, Beginning Balance	$ 402		$ 377
Liabilities Incurred	1		6
Liabilities Settled	(10)		(2)
Revision of Estimate	(1)		3
Accretion Expense	7	[1]	7	[1]
Asset Retirement Obligations, Ending Balance	$ 399		$ 391

[1] Accretion expense is included in DD&A expense in the consolidated statements of operations.